The cellular basis of ethanol action in the nervous system is poorly understood. Ethanol can affect the function of neurotransmitter receptors; however, the receptors in the central nervous system that are involved in the behavioral effects of ethanol have not been established. P2X receptors in bullfrog dorsal root ganglion neurons have been found to be inhibited by pharmacological concentrations of ethanol (Neurochem Intl 1999;35:143). P2X receptors are ligand-gated membrane ion channels that are activated by extracellular ATP. We studied the effect of ethanol on P2X4 receptors, the most common P2X receptor in the mammalian central nervous system. P2X4 receptors were expressed in Xenopus oocytes and their function was studied using two-electrode voltage-clamp. We found that the amplitude of current activated by 1 uM ATP was decreased by ethanol in a concentration-dependent manner over the concentration range 1-500 mM. The concentration of ethanol that produced 50% inhibition (IC50) of current activated by 1 uM ATP was 58 mM. Ethanol inhibition of ATP-activated current was not dependent on membrane potential from -60 to +20 mV, and ethanol did not change the reversal potential of ATP-activated current. Ethanol, 50 mM, shifted the ATP concentration-response curve to the right, increasing the EC50 for ATP from 9.1 to 16.0 uM, but ethanol did not reduce the maximal response to ATP. The results suggest that ethanol may inhibit P2X receptors by decreasing the apparent affinity of the binding site for ATP. Since the P2X4 receptor is the most abundant P2X subunit in the brain, these receptors could be important effectors of ethanol action in the central nervous system. Experiments are in progress studying the molecular basis of ethanol action on P2X4 receptors and the effect of ethanol on P2X receptors in central neurons.